Water exterts no pressure horizontally... only vertically dude. There might be a bit of static load but most pumps can deal with this. It also doesn't matter how big or small the container at the top or bottom is the weight of water never changes if it is above 4 degrees C. And exactly what Abyss said... what goes up must come down so it cancels out.

Water weighs .433 pounds per square inch per foot of height. You are correct about the head pressure... if you can only get 10 feet of head pressure and you have to go 11 feet you will have zero pressure. You can solve this problem by putting another pump back to back if you choose to increase head pressure or you can purchase a better pump.

If you need 10 psig to go 10 feet up and require 10psig at the top of 10 feet you need a pump that does 20psig. If you wanna get really technical you can also add in pressure reducing valves and an expansion tank and throw a bigger pump at it... hell throw in a lift check valve while your at it. :P